Stress is a documented risk factor for cardiac, metabolic, and neurological disease. How individuals respond to everyday stressors can interfere with whether they meet national guidelines for health behaviors such as exercise and sleep. The overarching goal of this project is to utilize an experimental medicine approach to develop an efficient, ecologically valid, within-person approach to measuring and intervening on the deleterious effects of everyday stress on meeting recommended levels of two health behaviors: physical activity and sleep patterns. In Phase 1, we will develop, validate and deliver a stress assay that assesses malleable components of the stress process that drive health behavior decisions and enactment as they unfold, in real-time and in individuals' natural environments. In Phase 2, we will use this assay to evaluate just-in-time intervention approaches that target specific stress response components at times and in contexts when they are most malleable and can positively impact health behaviors. In contrast to previous daily stress studies, we will conduct coordinated analyses in 10 intensive longitudinal datasets separating effects of stressor reactivity, recovery and pile-up on health behaviors. By replicating the results across 10 studies we will ensure identification of the most reliable and potent targets for intervention. The central hypothesis, drawn from stress theory, is that larger initial stressor reactivity, incomplete or slow recovery, and more frequent stress responses will negatively impact health behavior engagement. The rationale for the proposed research is that by identifying the strongest predictors of these health behaviors, stress interventions will be more effective in increasing physical activity and sleep to meet current guidelines (e.g. Center for Disease Control- promoted clinical recommendations). Specific aims extended from this hypothesis include: 1) Test the prediction across 10 intensive longitudinal datasets that stressor reactivity, recovery and pile-up can be identified and are more useful than traditional stress indices, 2) Test the prediction that these three components predict daily physical activity and sleep, 3) Identify characteristics of people who are either more at-risk (or resilient) to these stress interfering with health behaviors, 4) Validate these components in a novel sample, and 5) Test just-in-time interventions tied to times when individuals are vulnerable to the effects of stress. The research team has a history 10+ years collaboration and represents experts in theory, design, and analysis of daily stress and health behavior intervention. The approach is innovative because it tests theory- based predictions for health behaviors, will replicate effects across 10 datasets, and will develop and test novel and empirically-based just-in-time interventions from these results. The proposed research is significant by advancing our understanding of how stress influences the development of disease and by using interventions grounded in precision medicine to improve daily health behaviors to achieve their recommended levels.